1. Field of the Invention
The present invention relates to providing footwear with adjustable width to enable customized width fitting and adjustable width necessitated by changing conditions and activity during wear. The invention concerns, more particularly, articles of footwear having a longitudinal split midsole cooperating with a stretchable upper to enable dynamic fit adjustment.
2. Background of the Invention
Footwear sizing is generally based on the overall length of a wearer's foot with accommodation made for the width or girth of the foot as well. Footwear is generally purchased based on a static measurement of the wearer's foot without much regard to the change in the wearer's foot dimensions that may occur during a reasonable period of wear. Neither short term nor long term changes such as accommodation for the expansion of the foot at the end of a day, or growth of a child's foot within a few months from purchase are factored into the single static measurement at point of purchase.
The shape of the last on which the article of footwear is formed is the primary influence on the fit of an article of footwear. In general a last is made by taking the following foot measurements into account: the overall length of the foot, the width of the foot, the height of the first digit, the contour of the instep, and at least six girth measurements. The general practice is to shape a last for mass production by utilizing foot measurements from a broad spectrum of the population to determine the characteristics of a statistically average foot. This will theoretically achieve a proper fit for a majority of the population. Most footwear manufacturers only provide consumers with footwear in limited length-width combinations.
Prohibitive manufacturing and retail inventory challenges prevent mass manufacturers and marketers from offering footwear sizes in a full spectrum of length-width combinations. Since each length-width combination for an article of footwear generally requires a unique last that is correctly proportioned for that particular length-width combination, economics generally forces manufacturers and retailers to offer a limited spectrum of length-width combinations, based again, on a statistically average foot. The attempt is to cover as large a cross section of the population as possible. Research has demonstrated that this approach, while cost effective, yields little perceivable benefit to the consumer.
Many individuals do not have feet with statistically average proportions so the usual length-width combinations would not provide a proper fit. Some people have feet of left and right feet of different widths, such as the dominant foot being slightly larger. In addition, some individuals have foot proportions that change in a relatively short period of time. Children, for example, often experience rapid growth in the feet that prevent footwear from being worn for a significant portion of the footwear's useful life. Individuals with certain medical conditions, such as pregnancy or edema, may experience day to day changes in foot proportions. Any of these factors necessitate fit adjustment to enable the wearer to receive the full benefit of an athletic shoe in particular.
Due to these limitations, there have been multiple attempts in the prior art to provide for some measure of adjustment. The vast majority of prior art adjustment systems for footwear rely on some sort of mechanism for adjusting fit such as a lacing system, screw adjustments, or ratchet adjustments. The prior art sometimes combines the adjustment mechanisms in the midsole with inserts or other material variances to provide a measure of lateral or width adjustment.
Some prior art attempts to address width adjustment and fit employ articulating midsole and outsole units that are sized with interchangeable plugs. These systems do not allay the inventory problem since often the extra pieces must be inventoried and managed by a retailer.